Apparatus and methods for reducing plastics pipes

ABSTRACT

Apparatus and method for producing reduction in maximum width in plastics lining pipes includes at least one pair of reducing rolls through which the lining pipe is forced from upstream thereof. The rolls are disposed and configured to present a roll throat of effective ovality, defined by the percentage difference between the maximum dimension normal to the axes of rotation and the maximum dimension parallel to the axes of rotation, in the range of 5% and 30%.

BACKGROUND OF THE INVENTION

This invention relates to apparatus and methods for reducing the widthof plastics pipes, and more particularly to such apparatus and methodsfor reducing temporarily the width of plastics liner pipes for use inrelining old or damaged fluid transport pipelines, such as mains wateror drainage water pipelines.

The provision of such plastics liner pipes in these circumstances is aknown area of technology utilising a variety of ways of fitting theliner pipes into the existing pipework system. The present inventionrelates to a technique, hereinafter referred to as the "roll-down"technique, in which a liner pipe, either in a continuous length asformed on extrusion, or as separate plastics pipes butt-welded togetherto a continuous length, and having an appropriate width for eventuallyfitting tightly within the pipeline to be relined is pushed through asequence of roller sets to reduce the width of the liner temporarily sothat it may then be fed into and through the pipeline system to berelined and subsequently allowed to expand, possibly with the help ofpressurised fluids and/or heat, to its original width so as to fittightly within the original pipework.

In such a roll down system, the pipe liner is physically driven from theupstream end through a succession of curved profile rolls each of which,in end view, is somewhat half-circular in configuration, the basicprinciple being that the pipe liner, of larger diameter than a firstpair of opposed rolls having a somewhat circular roll throat in frontview, is, subject to the thrusting force from upstream, caused to reducein diameter on passage through that set of rolls, and then on through asecond pair of rolls, usually rotatable at right angles to the first setof rolls, and possibly even a third pair of rolls, again having theiraxes of rotation at right angles to the previous set of rolls.

It has been found in such an arrangement that a straightforwardreduction in diameter of the liner pipe in passing through a set of suchrolls, if the rolls exert a truly circular radial force on the incomingpipes, and therefore result in the output of a truly circular reducedpipe from the first rolls, can result in collapse of the pipe linerduring passage therethrough inwardly into a configuration generallyknown as a "heart collapse" (from its collapsed configuration of asomewhat heart-shaped nature). When this occurs, there is quite clearlya failure of the rolling technique.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome or at least tosignificantly reduce this problem.

According to one aspect of the present invention there is providedapparatus for producing reduction in width in plastics lining pipesincluding at least one pair of reducing rolls through which in use theliner pipe is forced from the upstream thereof, the rolls being disposedand configured to present a roll throat of effective ovality having apercentage of the difference between the maximum dimension normal to theaxes of rotation and the maximum dimension parallel to the axes ofrotation toward the last mentioned dimension in the range of 5% and 30%.

In accordance with another aspect of the present invention there isprovided a method for reducing in width plastics liner pipes forinserting into pipework comprising the steps of forcing the pipe fromupstream thereof through at least one pair of reducing rolls, beingdisposed and configured to present a roll throat of effective ovalityhaving a percentage of the difference between the maximum dimensionnormal to the axes of rotation and the maximum dimension parallel to theaxes of rotation toward the last mentioned dimension in the range of 5%and 30%.

The or each set of rolls may be freely rotatable.

With relatively small plastics liner pipes, which may preferably be madeof polyethylene, of initial diameter of the order of 4 inches (104 mmdiameter), two roll sets may be provided in succession with theirsuccessive axes of rotation at right angles, the rolls in each set maybe so disposed and configured as to present a reducing ovality at theroll throats of successive roll sets through the set. Thus where tworoll sets are provided, the first may be of the order of 13% to 18% forexample and the second may for example be of the order of 5% to 10%.

Again with initial diameter pipe of approximately 12 inches diameter(315 mm) the three sets of rolls each having axes of rotation at rightangles to the previous set may be provided, which may present a rollthroat ovality of between 22% and 25% for the first set of rolls, 14%and 18% for the second set of rolls, and 5% and 8% for the third set ofrolls.

Again with polyethylene pipe liners having an initial 18 inch diameter(450 mm) a three set draw down roll system may be provided in which thefirst set provides an ovality between 25% and 30%, the second setpresents an ovality of between 11% and 15%, and the third set providesan ovality of between 6% and 10%.

The overall width reduction produced by the above mentioned roll setswill be of the order of 10% of the original pipe liner diameter.

The Applicants are aware that in the roll reduction production of steeltube it has been proposed to apply slight ovality to the pipe undergoingreduction as it passes through the multiple roll sets in a sequence ofsuch sets of rolls. However, there are very significant differences inthe production of steel tube, in the operating speeds, and temperatures,as well as very different physical characteristics of the materials ofthe tubes and pipes concerned. Indeed, the technologies are not allanalogous. We have found that whereas the provided ovality in steel piperoll construction is of a minimal nature of the order of 1/2% ashereinabove defined, a surprisingly totally different order of ovality,with the highly desirable effects of strengthening the pipes against"heart collapse" with plastics liner pipes can be achieved in accordancewith the invention herein defined.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more readily understood oneembodiment thereof will now be described by way of example withreference to the drawing which is a schematic front view from downstreamof a pair of rolls 1, 2 through which a plastics liner pipe 3 is forcedfrom the upstream end.

DESCRIPTION OF THE INVENTION

The rolls 1, 2 are freely rotatable about axes 4, 5 and are profiled topresent a roll throat 8 of ovality defined by the percentage differencebetween the maximum dimension 6 normal to the axes 4, 5 and the maximumdimension 7 parallel to the axes 4, 5.

We have found that when roll reducing an initially 104 mm diameter linerpipe to a temporarily reduced liner pipe of general width of 89 mm(31/2inches ) a double roll set having axes at right angles to eachother and presenting successively a 16% ovality and a 7% ovalitysatisfactorily reduces the pipe width without any risk of collapse ofthe pipe liner in the manner herein described.

Similarly with a 315 mm initial diameter pipe a triple roll setpresenting a 23% ovality, a 16% ovality, and a 6.7% ovalitysuccessively, without risk of collapse of the pipe, produces atemporarily reduced pipe liner of general width of 290 mm.

Yet again, with a 450 mm diameter polyethylene pipe, a triple roll setpresenting successively a 27.5% ovality, a 13.8% ovality, and an 8%ovality produce a temporarily reduced pipe liner for insertion into thepipeline of general width of 423 mm.

It is to be understood that the foregoing is merely exemplary ofapparatus for and methods of reducing the width of liner pipes inaccordance with the invention and that modifications can readily be madethereto without departing from the true scope of the invention.

I claim:
 1. Apparatus for producing a reduction in width in plastics liner pipes including at least one pair of reducing rolls through which in use the liner pipe is forced from the upstream thereof, the rolls being disposed and configured to present a roll throat of effective ovality wherein the percentage of the difference between the maximum dimension normal to the axes of rotation and the maximum dimension parallel to the axes of rotation towards the last dimension is in the range of 5% and 30%.
 2. Apparatus as claimed in claim 1 wherein the or each set of rolls is freely rotatable.
 3. Apparatus as claimed in claim 1 wherein two roll sets are provided in succession with their successive axes of rotation at right angles, the rolls in each set being so disposed and configured as to present a reducing ovality at the roll throats of successive roll sets.
 4. Apparatus as claimed in claim 3 wherein, of the two roll sets provided, the effective ovality of the first is of the order of 13% to 18%, and of the second is of the order of 5% to 10%.
 5. Apparatus as claimed in claim 1 including three sets of rolls each having axes of rotation at right angles to the previous set, presenting an effective roll throat ovality of between 22% and 25% for the first set of rolls, 14% and 18% for the second set of rolls, and 5% to 8% for the third set of rolls.
 6. Apparatus, as claimed in claim 1 including a three set draw down roll system each set having axes of rotation at right angles to the previous set, wherein the first set provides an effective roll throat ovality of between 25% and 30%, the second set of between 11% and 15%, and the third set of between 6% and 10%.
 7. Apparatus as claimed in claim 6 wherein the overall width reduction produced by the above-mentioned roll sets is of the order of 10% of the original pipe liner diameter.
 8. A method for reducing a maximum width of plastic liner pipes for inserting into pipe work comprising the steps of forcing the pipe from upstream thereof through one pair of reducing rolls disposed and configured to present a roll throat of effective ovality having a maximum dimension less than the maximum original width of the liner pipe wherein the percentage of the difference between the maximum dimension normal to the axes of the rotation and the maximum dimension parallel to the axes of rotation toward the last mentioned dimension is in the range of 5% and 30%.
 9. Apparatus of claim 1 wherein the pair of reducing rolls contact substantially all of the plastic liner pipe circumference.
 10. Apparatus for producing a reduction in maximum width in plastic liner pipes including a pair of reducing rolls through which a liner pipe is forced from upstream thereof with the rolls being disposed and configured to present a roll throat having a maximum dimension normal to axes of rotation a percentage less than a maximum dimension parallel to the axes of rotation, the percentage defining an effective ovality, the effective ovality being in the range of 5% and 30%.
 11. Apparatus of claim 10 wherein the pair of reducing rolls contact substantially all of the plastic lining pipe circumference.
 12. Apparatus of claim 10 wherein the or each set of is freely rotatable.
 13. Apparatus of claim 10 wherein two roll sets are provided in succession with their successive axes of rotation at right angles, the rolls in each set being disposed and configured as to present a reducing effective ovality at the roll throats of successive roll sets.
 14. Apparatus of claim 10 wherein of the two roll sets provided the effective ovality of the first set is of the order of 13% to 18% and the second set is of the order of 5% to 10%.
 15. Apparatus of claim 10 comprising three sets of rolls each having axes of rotation at right angles to a previous set, presenting a roll throat having an effective ovality of between 22% and 25% for the first set of rolls, 14% and 18% for the second set of rolls, and 5% and 8% for the third set of rolls.
 16. Apparatus of claim 10 including a three set draw down roll system each set having axes of rotation at right angles to the previous set, wherein the first set provides a roll throat of effective ovality of between 25% and 30%, the second set between 11% and 15%, and the third set between 6% and 10%.
 17. Apparatus of claim 15 wherein the maximum width produced by the above mentioned roll sets is of the order to 10% of the original liner pipe diameter.
 18. The apparatus of claim 1, wherein the roll throat has a maximum dimension on the order of 31/2 inches or larger.
 19. The apparatus of claim 10, wherein the roll throat has a maximum dimension on the order of 31/2 inches or larger. 